Variable displacement vane pump and method of regulating the displacement thereof

ABSTRACT

A variable displacement rotary vane pump for fluids is provided where displacement regulation is achieved thanks to the variation of the relative eccentricity between a regulation ring ( 11 ) in which a rotor ( 13 ) is arranged and the rotor itself. In a region of engagement between the external surface ( 11 A) of the regulation ring ( 11 ) and the internal surface ( 40 A) of a chamber ( 40 ) inside which the regulation ring ( 11 ) moves, a plurality of rolling elements ( 25 ), mounted in fixed position, is provided. The rolling elements ( 25 ) are provided only over a portion of such a region of engagement, including a zone (S) where a resultant of mechanical and fluidic forces generated in the pump during the regulation acts. A method of regulating the displacement of such a pump is also disclosed.

TECHNICAL FIELD

The present invention relates to variable displacement rotary pumps, and more particularly it concerns a pump of a kind in which displacement regulation is obtained thanks to the variation of the relative eccentricity between a regulation ring and the pump rotor, obtained by varying the relative position of the ring and the rotor depending on the pump operating conditions.

The invention also concerns a method of regulating the displacement of such a pump.

Preferably, but not exclusively, the present invention is applied in a pump for the lubrication oil of a motor vehicle engine.

PRIOR ART

It is known that, in pumps for making lubricating oil under pressure circulate in motor vehicle engines, the capacity, and hence the oil delivery rate, depends on the rotation speed of the engine. Hence, the pumps are designed so as to provide a sufficient delivery rate at low speeds, in order to ensure lubrication also under such conditions. If the pump has fixed geometry, at high rotation speed the delivery rate exceeds the necessary rate, whereby high power absorption, with consequently higher fuel consumption, and a greater stress of the components due to the high pressures generated in the circuit occur.

In order to obviate this drawback, it is known to provide the pumps with systems allowing a delivery rate regulation at the different operating conditions of the vehicle, in particular through a displacement regulation. Different solutions are known to this aim, which are specific for the particular kind of pumping elements (external or internal gears, vanes . . . ). However, some general kinds of displacement regulation systems can be recognised and, in case of rotary vane pumps, one system is based on the variation of the relative position between an external regulation ring, also known as “stator ring”, inside which the rotor eccentrically rotates, and the rotor itself. A variation of the relative eccentricity of those components, and hence a variation of the pump displacement, is thus obtained.

This kind of regulation is implemented in different ways. Thus, it is possible to recognise:

-   -   pumps where the rotor causes rotation of the external ring to         which the radially outer ends of the vanes are hingedly         connected (“pendulum” pumps);     -   pumps where the stator ring can be displaced transversally to         the axis of rotation of the rotor;     -   pumps where the stator ring oscillates about an axis external to         the same ring; and     -   pumps where the stator ring is rotatable about an axis internal         to the same ring and parallel to the axis of rotation of the         rotor.

In such kinds of pumps, while the stator ring is being moved in order to vary the displacement, it is necessary to oppose its movement through means creating antagonist forces and generally consisting of springs. Such means opposing the movement of the stator ring generate problems of:

-   -   a) vibrations/noise, when an unstable equilibrium of the forces         and the frictions occurs during the movement;     -   b) generation of vibrations/pressure pulsations depending on the         fast transients of variation of the rotation speed and/or of the         regulation of the pressure thresholds;     -   c) hysteresis of the pressure regulation between the increase         and the decrease of the rotation speed;     -   d) wear due to an excessive specific pressure in the area where         the stator ring is supported.

In order to alleviate such problems, in case of a pump where displacement regulation is performed through a rotation of the stator ring, it has already been proposed to interpose rolling elements between an external surface of the stator ring and an internal surface of a chamber where the stator ring rotates. Clearly, by converting the sliding friction into rolling friction, the resistance to the stator ring rotation, on which hysteresis depends, is reduced.

An example is disclosed in U.S. Pat. No. 5,863,189, in which the external surface of the stator ring and the internal surface of the chamber form the inner and outer races of an annular roller bearing, in which the rollers are kept at the same mutual distance by a suitable annular cage. In this known solution, the cage with the rollers extends over the whole circumference of said surfaces and can be actuated only by means of a side lever arm which makes its construction complex.

Moreover, the Applicant has realised that an analysis of the mechanical and fluidic (in particular, hydraulic) forces which are generated during the pump operation shows that, in the pumps of the kind considered here, the resultant of such forces acts in a limited zone of the region of engagement between the external surface of the stator ring and the internal surface of the chamber in which the stator ring rotates and, therefore, it is in such a zone that is necessary to prevent generation of instable equilibriums or of equilibriums opposing the regulation movement in important manner.

DESCRIPTION OF THE INVENTION

It is an object of the present invention to provide a rotary positive displacement pump with variable displacement of the kind disclosed above, which obviates the drawbacks of the prior art.

According to the invention, this is achieved in that:

-   -   the rolling elements are provided only over a portion of a         region of engagement between the external surface of the         regulation ring and the internal surface of a chamber in which         the ring moves, said portion including a zone where a resultant         of mechanical and fluidic forces generated in the pump during         the regulation acts and where a fluidic support bearing is         generated due to the effect of such a resultant; and     -   the rolling elements are arranged, in said portion of the region         of engagement between said surfaces, so as to be movable as an         integral body along said surfaces during the regulation         movement, the movement of the rolling elements having a smaller         amplitude than a movement performed by the regulation ring in         order to make the pump pass from a maximum displacement         condition to a minimum displacement condition.

Preferably, the regulation movement is a rotation, the portion of the region of engagement between the surfaces is configured as a sector of a rolling bearing of which said surfaces form sectors of the inner race and the outer race, respectively, and the rolling elements are arranged within a seat formed in the external surface of the regulation ring.

According to another preferred feature of the invention, the rolling elements are rollers or needles mounted in a supporting and guiding cage arranged to move in said seat against the action of an opposing resilient member, which is arranged between one end of the cage and one end of the seat and is preloaded so as to keep the cage in contact with the opposite end of the seat in a maximum displacement or rest condition of the pump.

The invention also provides a method of regulating the displacement of a pump of the above kind, comprising the steps of:

-   -   providing a plurality of rolling elements over a portion of a         region of engagement between an external surface of the         regulation ring and an internal surface of a chamber in which         the ring moves for the regulation, such a portion including a         zone where a resultant of mechanical and fluidic forces         generated in the pump during the regulation acts and where a         fluidic support bearing is generated due to the effect of such a         resultant; and     -   during the regulation movement, making the rolling elements move         as an integral body in said portion of the region of engagement         between said surfaces, the movement of the rolling elements         having a smaller amplitude than a regulation movement making the         pump pass from a maximum displacement condition to a minimum         displacement condition.

BRIEF DESCRIPTION OF THE FIGURES

The above and other features and advantages of the invention will become apparent from the following description of a preferred embodiment, made by way of non limiting example with reference to the accompanying drawings, in which:

FIG. 1 is a view showing a vane pump in which the invention can be applied, without the closure cover and in the maximum displacement condition;

FIG. 2 is a view similar to FIG. 1 and shows the same pump in the minimum displacement condition;

FIG. 3 shows the magnitudes and the directions of the main forces intervening during the operation of the pump shown in FIGS. 1 and 2, of their partial resultants and of the overall resultant in the maximum displacement condition of the pump, at the start of the displacement regulation;

FIG. 4 is a view similar to FIG. 1 and shows the magnitudes and the directions of the forces, of their partial resultants and of the overall resultant in the minimum displacement condition, at the end of the displacement regulation;

FIGS. 5 and 6 show a pump according to the invention, in maximum and minimum displacement conditions, respectively;

FIG. 7 is an enlarged isometric view of the roller-carrying cage shown in FIGS. 5 and 6; and

FIG. 8 is an exploded isometric view of the pump according to the invention.

DESCRIPTION OF PREFERRED EMBODIMENTS

By way of example only, in the Figures there is considered a pump where the displacement variation is achieved through the rotation of the regulation stator ring (hereinafter referred to as “stator” for the sake of brevity) about an axis parallel to the axis of rotation of the rotor and where the rotation of the stator is directly controlled by the pressure of the pumped fluid.

Referring to FIGS. 1, 2 and 8, a pump 1 of the above kind comprises a body 10 having a suitably shaped cavity 40 in which stator 11 is mounted so as to be freely rotatable along an arc of circumference, in the illustrated example in clockwise direction, as indicated by arrow A. Reference character B denotes the axis of rotation of stator 11. Stator 11 has a chamber 12 where vane rotor 13 is housed. The rotor is keyed on a shaft 14 arranged off-axis relative to centre C of chamber 12. Also rotor 13 is rotatable in clockwise direction. Reference numerals 41 and 42 denote the ends of the suction and delivery ducts, when rotor 13 rotates in clockwise direction.

As known to the skilled in the art, rotation of stator 11 about axis B causes a variation of the relative eccentricity between stator 11 and rotor 13, and hence a variation of the displacement, between a condition of maximum eccentricity and displacement (shown in FIG. 1), which is taken also in rest conditions of the pump and in which rotor 13 is substantially tangent to surface 12A of chamber 12, and a condition of minimum displacement (shown in FIG. 2), in which rotor 13 is coaxial or substantially coaxial with chamber 12. Such an arrangement is wholly conventional and a more detailed description is not required.

In the example illustrated, for the control of its rotation, stator 11 has a pair of radial appendages 17, 18, which project into respective chambers 15, 16 formed by recesses of cavity 40, and which slide in fluid-tight manner on the bases of chambers 15, 16. One of the chambers, for instance chamber 15, is permanently connected to the delivery side of the pump or to the units utilising the pumped fluid (in particular, in the preferred application, to a point of the engine lubrication circuit located downstream the oil filter), through a first regulation duct, not shown in these Figures. The other chamber can in turn be put in communication with the delivery side or with the units utilising the pumped fluid through a valve operated by the electronic control unit of the vehicle and a second regulation duct (not shown). In this manner, appendage 17 is, or both appendages 17, 18 are, exposed to the pressure conditions of the pumped fluid.

An end wall of one of the chambers, e.g. chamber 15, may be shaped so as to form an abutment 19 for appendage 17 in the maximum displacement condition.

Chamber 16 houses a member 20 opposing the rotation of stator 11. That member, in the example illustrated, comprises two opposite mushroom-shaped elements 21, 22, connected for instance in telescopic manner and biased in opposite directions by a spring 23 arranged between heads 21A, 21B of both elements. Spring 23 is preloaded so as to oppose the rotation of stator 11, and hence to keep it in the position shown in FIG. 1, as long as the pressure applied to appendage 17 (or the overall pressure applied to appendages 17, 18) is lower than a predetermined threshold, and to subsequently keep the pump displacement at the value corresponding to the pressure threshold. Such a condition is attained when an equilibrium is established between the torques generated by the pressure acting on appendages 17, 18 and the antagonist torque generated by spring 23.

Heads 21A, 21B, for instance substantially shaped as half cylinders, engage recesses 22A, 22B of complementary shape formed in the opposite surface of appendage 18 with respect to the surface acted upon by the regulating pressure and in a wall of chamber 16, respectively. Thus, a pair of articulated joints is formed allowing keeping the ends of spring 23 mutually parallel during the rotation of stator 11, thereby ensuring a good lateral stability of the spring itself.

The circumferential extension and the radial size of chambers 15, 16 will be determined depending on the operation characteristics required of the pump. In particular, as far as the circumferential extension is concerned, a rotation of stator 11 of the order of about 20° is typical for the preferred application and has been shown in the drawings. As to the radial size, it may be constant over the whole circumferential extension, so that appendages 17, 18 have a constant thrust area and hence generate a constant torque, proportional to the actuation pressure, over the whole arc of rotation. In the alternative, the radial size of one chamber or both chambers may change along the circumferential extension, and appendages 17, 18 have a variable thrust area, so as to generate a variable torque over the arc of rotation of stator 11. Such a solution allows taking into account the fact that the resistant torques encountered during displacement regulation may be variable, for instance because the resistance opposed by opposing spring 20 and/or the rotational frictions vary.

FIGS. 1 and 2 also show the different forces acting on the components of pump 1 during operation and the reactions caused by such forces. It is to be appreciated that FIGS. 1 and 2 only are intended to give a representation of the zones where the different forces act and of the directions of the forces, whereas their magnitudes are not considered. More particularly:

-   -   F_(P1), F_(P2) are the thrust forces applied to appendages 17,         18 by the fluid introduced into chambers 15, 16; it is assumed         that the fluid under pressure is introduced into chamber 16         during regulation, that is why force F_(P2) is shown only in         FIG. 2;     -   F_(M) is the force opposing the rotation of stator 11 applied by         opposing member 20;     -   F_(ATT) is the frictional force between heads 21A, 22A of         elements 21, 22 forming member 20 and the respective seats 21B,         22B;     -   F_(HYD) is the force applied on rotor 13 and stator 11 by the         fluid present in pumping chamber 12;     -   F_(C) is the force opposing F_(HYD) exerted by body 10;     -   R_(V) is the hydraulic reaction to the resultant of the forces         mentioned above;     -   R_(H) is the friction between stator 11 and the internal surface         40A of chamber 40 during the rotation of stator 11.

FIGS. 3 and 4 show the vectors representing forces F_(P1)-F_(C) mentioned above and their partial and overall resultants in the extreme operating conditions shown in FIGS. 1 and 2. In FIGS. 3 and 4, the origin of the axes coincides with centre of rotation B of stator 11. As it clearly appears from a superposition of the diagrams on the right side of FIGS. 3 and 4 onto FIGS. 1 and 2, respectively, resultants SV1 and SV2, respectively, of the above forces have such orientations that they act in correspondence of a zone S of the mutually engaging surfaces in stator 11 and cavity 40. In this zone, by reaction, the fluid under pressure present in chamber 12 creates a hydraulic support bearing. The reaction provided by such a bearing is force R_(V) mentioned above, which has the same magnitude as and opposite direction to the above resultants.

In order to optimise the pump operation, it is necessary to minimise irregularities and jamming during the movement of stator 11 and the resultant vibrations, noise and hydraulic pulsations in zone S where resultants SV1, SV2 act. The remaining portion of the region of engagement between surfaces 11A, 40A has a far lower influence and does not require particular interventions.

This optimisation is obtained by means of the pump according to the invention, which will be now described with reference to FIGS. 5-8. Elements already disclosed with reference to FIGS. 1 and 2 are denoted by the same reference numerals.

According to the invention, a plurality of rolling elements 25, in the illustrated example rollers or needles (herein below generally referred to as “rollers”), are arranged between external surface 11A of stator 11 and internal surface 40A of cavity 40, over a portion including zone S where the hydraulic support bearing is created and where resultants SV1, SV2 of the various forces act. In correspondence of such a portion a sector of a rolling bearing is thus formed, of which external surface 11A of stator 11 forms the corresponding sector of the inner race whereas internal surface 40A of cavity 40 forms the corresponding sector of the outer race. Rollers 25 are fitted, for instance snap fitted, in respective seats 27 in a supporting cage 26, preferably made of plastic material, which in conventional manner acts as a guide and a spacer for rollers 25.

Cage 26 with rollers 25 is housed in a recess of external surface 11A of stator 11, which recess axially extends over the whole axial depth of stator 11 and chamber 40. Recess 28, cage 26 and rollers 25 have such a radial size that the contact between surfaces 11A and 40A is ensured by rollers 25. Typical diameters for the rollers, in the preferred application, are of the order of a few millimetres, for instance 2-4 mm. Also cage 26 axially extends over the whole depth of stator 11, whereas rollers 25 have an axial size (length) slightly shorter than that of cage 26. This gives a labyrinth configuration to the assembly of cage 26 and rollers 25, which configuration allows maintaining the hydraulic support bearing.

Cage 26 has an angular extension smaller than the angular extension of recess 28, so that it can move within the recess during the rotation performed by stator 11 for the displacement regulation, and the angular extension of the displacement of cage 26 is smaller than the angular extension of the rotation performed by stator 11 for passing from the maximum displacement position to the minimum displacement position. Considering that only surface 11A moves and taking into account the difference in the radiuses of moving surface 11A and stationary surface 40A, the solution described, in which seat 28 for cage 26 is formed in the moving part, allows rollers 25 to displace over a same distance on both surfaces, and hence to rotate without sliding.

Recess 28 is defined by two steps or abutments 29A, 29B. One end of cage 26 abuts against one of such abutments, for instance abutment 29A, in the rest condition (maximum displacement) of the pump, shown in FIG. 5. A resilient member 30 opposing the cage movement, e.g. a suitably preloaded leaf spring, is instead arranged between cage 26 and the other abutment 29B and it keeps cage 26 in contact with abutment 29A in the maximum displacement condition.

FIGS. 5 and 6 clearly show the behaviour of cage 26 with rollers 25 during displacement regulation. In order to make understanding easier, three reference points belonging to body 10, stator 11 and cage 26, respectively, have been shown by segments X, Y and Z. The three points are chosen so that their positions coincide in the maximum displacement condition (FIG. 5). At the end of the rotation bringing stator 11 to the minimum displacement position (FIG. 6), point X of course has remained stationary, whereas point Z has displaced in clockwise direction and has described an arc that, in the example illustrated, is of about 20°. Also point Y has performed a rotation in clockwise direction, yet over an arc shorter than that described by point Z. Due to the shorter rotation of cage 26 with respect to stator 11, cage 26 is no longer in contact with abutment 29A at the end of the rotation and spring 30 is more compressed.

It is clear that the invention obviates the drawbacks mentioned above of the prior art. Actually, the provision of rolling elements 25 between engagement surfaces 11A, 40A reduces per se the friction with respect to the case when stator 11 is supported by the only hydraulic bearing. Moreover, configuring the region of engagement between the surfaces as a sector of a bearing (or an open bearing), extending in the zone where the resultant of the mechanical and hydraulic forces generated during the regulation acts, avoids the jamming due to such forces. Lastly, arranging rolling elements 25 so that they can move within a seat 28 formed in stator 11 over a distance shorter than that over which the stator itself has moved prevents rolling elements 25 from sliding and hence reduces the resistance to the regulation movement.

It is clear that the above description is given only by way of non-limiting example and that changes and modifications are possible without departing from the scope of the invention.

For instance, even if there has been shown in detail a pump where displacement regulation is performed through a rotation of the stator about an axis internal to the stator itself and said rotation is directly controlled by the pressure of the pumped fluid, the invention can be applied also to pumps where the rotation of the stator is achieved in different manner (for instance, through a gear engaging a toothed sector of the external surface of the stator, like in U.S. Pat. No. 5,863,189) or to pumps where the regulation movement is different from the rotation of the stator disclosed here (“pendulum” pumps, pumps with oscillating stator, pumps with a translation of the stator ring, and so on). Of course, if the regulation movement performed by the stator is a translation, cage 26 will be a linear cage. 

1. A variable displacement rotary vane pump for fluids, comprising: a rotor (13) arranged to eccentrically rotate within a regulation ring (11) with a relative eccentricity which varies depending on operating conditions of the pump (1); means (17, 18) for moving the regulation ring (11) in a chamber (40) formed in a pump body (10) in order to vary said relative eccentricity, and hence the displacement of the pump, as said operating conditions vary; and a plurality of rolling elements (25) interposed between an external surface (11A) of the regulation ring (11) and an internal surface (40A) of the chamber (40); characterised in that: the rolling elements (25) are mounted in a supporting cage (26) and are provided only over a portion of a region of engagement between the external surface (11A) of the regulation ring (11) and the internal surface (40A) of the chamber (40), said portion including a zone (S) where a resultant (SV1, SV2) of mechanical and fluidic forces generated in the pump during the regulation acts; and the rolling elements (25) and said supporting cage (26) are arranged, in said portion of the region of engagement between said surfaces (11A, 40A), so as to move as an integral body along said surfaces (11A, 40A) during the movement of the regulation ring (11), the movement of the rolling elements (25) and of the supporting cage (26) having a smaller amplitude than a movement performed by the regulation ring (11) in order to make the pump pass from a maximum displacement to a minimum displacement.
 2. The pump as claimed in claim 1, wherein the regulation movement is a rotation of the regulation ring (11) and wherein: in said portion of the region of engagement, the external surface (11A) of the regulation ring (11) and the internal surface (40A) of the chamber (40) form, together with the rolling elements (25), a sector of a rolling bearing of which said surfaces form sectors of an inner race and an outer race, respectively; and the rolling elements (25) are arranged within a seat (28) formed in the surface (11A) of the regulation ring (11) and having a greater extension than the supporting cage (26) in which the rolling elements (25) are mounted.
 3. The pump as claimed in claim 2, wherein the supporting cage (26) is arranged to move in said seat, thereby moving the rolling elements (25), against the action of an opposing resilient member (30), which is arranged between one end of the cage (26) and one end (29B) of the seat (28) and is capable of keeping or bringing again the cage (26) in contact with an opposite end (29A) of the seat (28) in the maximum displacement condition of the pump.
 4. The pump as claimed in claim 3, wherein the rolling elements (25) are mounted in the supporting cage (26) so as to give it a labyrinth configuration arranged to maintain a fluidic support bearing generated in said zone (S) as a reaction to the action of the resultant (SV1, SV2) of said forces.
 5. The pump as claimed in claim 4, wherein the rolling elements (25) are rollers or needles, and wherein the supporting cage (26) has an axial depth substantially corresponding to an axial depth of the regulation ring (11) and the rollers or needles (25) have a length shorter than the axial depth of the cage (26).
 6. The pump as claimed in claim 1, wherein the rotation of the regulation ring (11) is directly controlled by the pressure of the pumped fluid.
 7. The pump as claimed in claim 1, wherein the pump is a pump for the lubrication circuit of a motor vehicle engine.
 8. A method of regulating the displacement of a rotary variable displacement pump for fluids, of a kind comprising a rotor (13) arranged to eccentrically rotate within a regulation ring (11) with a relative eccentricity that is variable depending on operating conditions of the pump (1), the method comprising the steps of: providing, between an external surface (11A) of the regulation ring (11) and an internal surface (40A) of a chamber (40) housing the ring (11), a plurality of rolling elements (25) mounted in a fixed relative position; and making the regulation ring (11) move in the chamber (40) in order to vary said relative eccentricity, and hence the displacement of the pump, as said operating conditions vary; and being characterised in that the step of providing rolling elements (25) in the chamber (40) comprises the steps of: providing the rolling elements (25) mounted in a supporting cage (26) only over a portion of a region of engagement between the external surface (11A) of the regulation ring (11) and the internal surface (40A) of the chamber (40), said portion including a zone (S) where a resultant (SV1, SV2) of mechanical and fluidic forces generated in the pump during the regulation acts; and during the regulation, making the rolling elements (25) and the supporting cage (26) move as an integral body in said portion of the region of engagement between said surfaces (11A, 40A), the movement of the rolling elements (25) and the supporting cage (26) having a smaller amplitude than a movement of the regulation ring (11) making the pump pass from a maximum displacement to a minimum displacement.
 9. The method as claimed in claim 8, wherein the regulation movement is a rotation of the regulation ring (11) and the step of providing the rolling elements (25) and the supporting cage (26) only over a portion of the region of engagement between said surfaces (11A, 40A) comprises the step of configuring the rolling elements (25) and the supporting cage (26), the external surface (11A) of the regulation ring (11) and the internal surface (40A) of the chamber (40) as a sector of a rolling bearing, of which said surfaces form circular sectors of an inner race and an outer race, respectively.
 10. The method as claimed in claim 9, wherein the step of making the rolling elements (25) and the supporting cage (26) move as an integral body comprises moving the rolling elements (25) and the supporting cage (26) in a seat (28) formed in the surface (11A) of the regulation ring (11) and having a greater extension than an overall extension of said rolling elements (25) and said supporting cage (26).
 11. The method as claimed in claim 8, wherein the step of making the rolling elements (25) and the supporting cage (26) move as an integral body comprises moving the rolling elements (25) and the supporting cage (26) in a seat (28) formed in the surface (11A) of the regulation ring (11) and having a greater extension than an overall extension of said rolling elements (25) and said supporting cage (26).
 12. The pump as claimed in claim 2, wherein the rolling elements (25) are mounted in the supporting cage (26) so as to give it a labyrinth configuration arranged to maintain a fluidic support bearing generated in said zone (S) as a reaction to the action of the resultant (SV1, SV2) of said forces.
 13. The pump as claimed in claim 12, wherein the rolling elements (25) are rollers or needles, and wherein the supporting cage (26) has an axial depth substantially corresponding to an axial depth of the regulation ring (11) and the rollers or needles (25) have a length shorter than the axial depth of the cage (26).
 14. The pump as claimed in claim 2, wherein the rotation of the regulation ring (11) is directly controlled by the pressure of the pumped fluid.
 15. The pump as claimed in claim 1, wherein the supporting cage (26) is arranged to move in said seat, thereby moving the rolling elements (25), against the action of an opposing resilient member (30), which is arranged between one end of the cage (26) and one end (29B) of the seat (28) and is capable of keeping or bringing again the cage (26) in contact with an opposite end (29A) of the seat (28) in the maximum displacement condition of the pump.
 16. The pump as claimed in claim 15, wherein the rolling elements (25) are mounted in the supporting cage (26) so as to give it a labyrinth configuration arranged to maintain a fluidic support bearing generated in said zone (S) as a reaction to the action of the resultant (SV1, SV2) of said forces.
 17. The pump as claimed in claim 16, wherein the rolling elements (25) are rollers or needles, and wherein the supporting cage (26) has an axial depth substantially corresponding to an axial depth of the regulation ring (11) and the rollers or needles (25) have a length shorter than the axial depth of the cage (26).
 18. The pump as claimed in claim 15, wherein the rotation of the regulation ring (11) is directly controlled by the pressure of the pumped fluid.
 19. The pump as claimed in claim 1, wherein the rolling elements (25) are mounted in the supporting cage (26) so as to give it a labyrinth configuration arranged to maintain a fluidic support bearing generated in said zone (S) as a reaction to the action of the resultant (SV1, SV2) of said forces.
 20. The pump as claimed in claim 19, wherein the rolling elements (25) are rollers or needles, and wherein the supporting cage (26) has an axial depth substantially corresponding to an axial depth of the regulation ring (11) and the rollers or needles (25) have a length shorter than the axial depth of the cage (26). 